Urea resin type molding composition and process of making same



Patented Aug. 9, 1938 PATENT OFFICE UREA RESIN .TYPE MOLDING COMPOSITION AND PROCESS OF MAKING SAME Carleton Ellis, Montclair, N. 1., assignor to Ellis- Foster Company, a corporation of New Jersey No Drawing.

Application June 15, 1935,

Serial No. 26,826

2 Claims.

The present application is a continuation-inpart of application Ser. No. 1,698 filed January 14,1935, in continuing the subject matter thereof which relates to the subjection of urea-formalde- 5 hyde resins to the action of pressure prior to shaping before molding, and of application Ser. No. 426,192 filed February 5, 1930 insofar as it continues the subject matter relating to the impregnation of cellulose with urea resins under pressure prior to molding. The invention claimed in application 426,192 is directed primarily to the use of urea-formaldehyde resins in the manufacture of veneers. Application 1,698 continues from application 689,165 the idea of subjecting urea-formaldehyde resins to the action of differential rolls prior to molding. The present case, therefore, continues this subject matter from application 689,165 and to this extent is a continuation-in-part of that application as well as of U. S. Patent 1,536,881 which was co-pending with application 689,165. The invention claimed in application 689,165 is directed primarily to acid resiniiied urea-formaldehyde resins.

The object of the present invention is to subject urea-formaldehyde resins prior to molding to the action of pressure in order to make said resins more amenable to molding under pressure.

As most molding compositions of the urea resin type include additions of cellulose as a filler which,

by the way, as I have noted in previous applications probably involves a reaction in the nature of formation of a chemical compound designated urea resin cellulosate, conditions of hydration arise which are quite difierent from those obtaining in the preparation of molding compositions from the customary anhydrous phenolformaldehyde resins. In the latter case the reaction in making the resin is ordinarily carried to the point where a separation of crude resin from the aqueous portion of any formalin used results, permitting the production of a substantially anhydrous resin stock which may then be incorporated with cellulose fiber. On the other hand, the pronounced hydrophilic properties of urea resin in those stages of preparation which permit the introduction of cellulose as a filler necessitate the presence of considerable water arising from formalin and a resultant swelling of the cellulose fibers comes about.

to produce a dried composition of a very voluminous character. For example, when ground in a ball mill such a powder may have a specific volume of 250 to 2'75 cc., that is, 100 grams of the composition will evidence this bull; as con- This tends (o1. lac-22') trusted with a corresponding weight of water. Conditions, therefore, obtain in the production of urea resin molding compositions which do not appear when phenol-formaldehyde molding compositions are prepared.

The present invention seeks in part to embrace methods which will approximately offset the swelling and voluminizing eilwt of water on cellulose and which will provide a densified and compact material of such density that the cavi- 10 ties of molds used in the operation of making molded articles do not have to be made unduly large. The present process enables molds which are now used for phenol-formaldehyde compositions to be readily and usefully employed for 15 molding urea resin products.

Since one particular virtue of urea resin molding compositions is the fact that the resin itself is light colored or water white and light stable, molded articles may be made which are white 20 or ivory or of delicate shades of color. To meet requirements of.this sort, however, calls for the use of a cellulose filler which in itself is white and for such purposes the highly refined cellulose known as alpha stock or bleached sulphite pulp 25 and the like may be used advantageously. However, such stock usually has to be comminuted in a powerful shredding machine before use and this in itself tends to create a filler which is of a voluminous character and such condition, to- 30 gether with the swelling effect due to water, produces a composition having far too great a bulk to be molded directly.

One method which has been adopted to permit densiflcation is to compress the ground material 35 in a pilling type of apparatus and then crush the pilled material and use the granulated product. This secures a good degree of densiflcation but does not allow of the escape of certain gases or gas-forming agents which are present in or 40 are occluded by the composition as a result of the process of manufacture. Hence, when such material is molded, especially in deep or complicated molding cavities, gas may collect in remote parts of the mold causing blistering of the tion is densified by warm milling rolls and the like, a substantially complete elimination of the gas-forming substances, such as water, methyl alcohol, and so forth, results, providing a composition which may be molded directly in molds without any such measure of gas evolution as will cause the molded article to be impaired in appearance or strength and yielding a product which will mold with the ease and trouble-free character of well-made phenolic compositions.

The present invention is particularly concerned with mlllng or macerating attrition as a form of impregnation and densification which, as indicated above, may be carried out by passing the stock through milling mils or other kindred types of. mils such as those of the Banbury mixer. The various sorts of mils used for the purpose may be suitably heated and in some cases I may I it through warm milling mils a charge of wet material which is rolled and remlled until moisture, excess formaldehyde, and so forth, have been eliminated. In other words, the wet composition before being introduced into the dryer is passed through steam-heated mils, preferably arranged in the form of a train so that the product passes fmm roll to roll and is densified into thin flakes which, if desirable, may be oven dried to reduce moisture to the desired point. In this connection it may be stated that I prefer the total water content, both mechanical and chemical, of the composition in finished form not to exceed about 8 per cent, of which preferably less than one-half may be mechanical and the balance chemical. A determinationof water content may be made by heating, for example, 25 grams of the composition in 250 cc. of nlol, using a condenser which returns the xylol but permits collection of the water. By reading the volume of water obtained in the first portion the mechanical water can be readily calculated, while the later portion coming over when the xylol has .been heated to the curing temperature of the composition may be expressed as chemical water.

Another procedure is to eliminate most of the water by drying before subjecting the composition to rolling attrition. Thus the material hot from the driers is subjected to the action of differential rolls where the usual heavy pressure and attrition of such milling rolls is exerted. Since one mil in a differential train of this type revolves faster than another to which it is juxtaposed, a milling action under heavy pressure re suits and the material undergoing the milling treatment is roll-ground and well densiiled. Further densification occurs in the compression caused by sheeting rolls when these are used. Owing to the pressure and stresses exerted by the differential rolls they quickly become heated and therefore the temperature ofthe milling mass is raised above room temperature, which aiIords opportunity for the progress of condensation and degasification.

Rolling attrition can also be carried out in the following way. The material as it comes from the driers is ground to a fine powder in a ball mill and the necessary quantities of pigment, accelerator and mold lubricant are added. The powder thus obtained is placed in a mixer where it is subjected to the action of mixing mils or revolving blades that squeeze the material against the walls of the mixer and where, at the same time, a hydraulic ram forces the charge into the mixer, causing a pressure to be exerted on the composition at the point of milling attrition of, say, to 1000 pounds per square inch while the consolidating and homogenizing effect progresses. The temperature in the mixer is preferably kept below about 80 C. and the pressuremixing is continued until the material is in the form of firm granules. Gaseous products generated by this treatment are allowed to escape, for example through an annular opening around the ram shaft. When properly consolidated and degaslfied the material is discharged and is ready for hot-pressing.

Numerous modifications are possible in the foregoing manner of procedure. For example, the urea cellulose product coming wet from the mixers may be dried and the crumbs of dried material may then be mixed with a dye or pigment, a mold lubricant, and so forth, and the mix subjected to rolling attrition. The crushing or macerating action under the heat and pressure of rolling attrition causes good intermingiing of the color with the urea resin cellulose stock accompanied by a densification of the material. After such treatment the product may be readily comminuted as, for example, by projecting it in a strong air blast against a resistant surface. Thus comminuted the powder may be used directly for molding or may be granulated, preformed, or otherwise be suitably prepared for the final step of molding.

Under treatments such as the above the condensation reaction is partly advanced and the volatiles present or thereby engendered are sufficiently eliminated; this further condensation, of course, being kept below the point at which products of deficient flow result. cedure a composition from which undesirable gaseous compounds are removed and at the same time one of suitably densiiled nature is obtained. The degasiflcation and densification can be carried out in any kind of apparatus where pressure can be exerted and volatiles eliminated. In machines where heat-treatment under pressure occurs in a more or less confined space, it may be necessary to contml the frictional heat by suitable means so as to prevent the temperature fmm reaching an unduly high point and precuring the resin. In cases where the pressure-mixing is done, for example, on exposed rolls the temperature may be kept at any desired point by continuous heating, for example, by steam or hot water circulation in the mils.

Thus it is possible by the rolling attrition referred to above to obtain a consolidated mass compacted to a volume approximately one-half that of the ordinary powder and such material when crushed to form granules will exhibit a speciilc volume of to 150, which represents a density adequate for most molding operations and which'compares favorably with the density obtained more simply by the employment of the easily made, substantially anhydrous phenolformaldehyde resins. At the same time the pressure to which the cellulose urea resin is exposed in this way tends to improve the translucency of the resulting molded article. From this standpoint a vacuum treatment followed by pressure represents an alternative procedure, as will be later discussed.

Preferably an aqueous urea resin syrup, diluted with water or undiluted, as the case may be, is mixed with the cellulose. Thorough impregnation is important in order to secure that change in the character of the cellulose which results in the production on hot pressing of translucent articles. Impregnation of cellulose fiber may be conducted by a vacuum and pressure By this prov a 9,190,077 process, that is, the fiber as such or in paper form.

or otherwise is placed in a closed receptacle and the air withdrawn to produce a high vacuum. The urea resin impregnating syrup then is run into the receptacle and pressure is applied. In this way the fibers are better impregnated. This is desirable in. particular when paper of some thickness is used. Impregnation adequate to fill the canals of the fibers in a substantially complete manner tends to yield the highest degree of transparency or translucency in the finished molded article or laminated sheet. A vacuum of. for example, -25 inches or thereabouts of mercury may be employed, followed by a pressure of 50-100 pounds or higher, as desired.

Commercial formaldehyde solution is generally used because this represents the cheapest form in which the aldehyde is' obtainable. The reaction with urea and the formalin maybe carried out in the cold (at room temperature or lower) or it may be eflected by heating to the boiling point or to various intermediate temperatures. The time required at the higher temperatures is correspondingly shorter but for some purposes reaction in the cold, that is, at room temperature or under artificially refrigerated conditions may be carried out. The color of the molded article" generally is days or more may be found necessary.

Commercial formaldehyde is usually about 37" to 40 per cent strength as furnished to the market in the United States and contains a small percentage of free acid which reckoned as formic is about 0.02 to 0.06 per cent. The reaction between urea and formaldehyde is influenced by the proportion of acid present and while I prefer to carry out the reaction under conditions which are rather on the acid than the alkaline side, nevertheless a reduction in the acidity of the crude formalin is desirable. This may be carried out by using neutral formalin of a pH of '1. Another method is to react the formalin with the cellulose filler, when the latter'is to be used, as is generally the case, to adsorb the formic acid. Thus by mixing cellulose filler and formalin solution and allowing them to stand for a period of several hours a very substantial reduction in acidity as measured by pH occurs. For example, formalin having an; acidity represented by pH 2 will drop to an acidity -of pH, say 6 or 6.5. when adsorption of formic acid by the filler has proceeded sufficiently, urea may be introduced and reacted in the cold or by heating, if desired. Sometimes magnesium carbonate and the like may be added to prevent too highly .acid conditions.

liminary step of exposing it to the action of formalin but instead the urea and formalin have been reacted either hot or cold, the filler is charged into the reaction solution and is agitated until good mixture results. If the urea resin solution at this stage is too thickand syrupy for good penetration into the cellulose fiber, dilution with a limited proportion of watermay be employed to assist, in

conjunction with vacuum and pressure impregnation, workingcn rolls and the like. customarily eral pigment, such as also I prefer to add a for D0! cent of a white mintltanium oxide or lithopone to act as a destarching agent, as described in pending applications; the addition of the destarching agent may, however,be postponed if desired until the later stage of grinding is in order.

In the production of urea resin molding compositions meeting a broad range of commercial requirements a careful control of all the factors entering into the manufacture of the material is necessary. Since the usual colors are either white, ivory. or of very light tints, any dust or dirt getting into the batch will cause an unfavorable appearance of the molded article. Hence freedom from dust in the various stages of manufacturing is necessary.

, Rolling attrition generally tends to improve the rate or speed of cure. often raising the rate by 25 to 35 per cent. This is an improvement of importance in practical molding, where great output is essential.

Another result'achieved in the. employment of rolling attrition to prepare the molding composition in suitable densifled form is that apparently a moreheat-elastic product can be obtained. In some cases articles which have threads molded thereon. such as bottle caps, cannot be removed from the mold except by unscrewing the molded piece, a dimculty which is aggravated if high molding temperatures are desired to obtain rapid production. The densifled material made by roll-,

article is still hot. Such a stripping operation cannot be carried out if the threads are very deep but if shallow the article may be molded at a relatively high temperature and be stripped from the mold before burning sets in. Compositions of this character, therefore, permit of a much greater production of such molded goods than could be accomplished otherwise.

The feature which constitutes the preferred embodiment of the present invention is that of COD:- duct of at least a part of the step of reacting urea and formaldehyde or the products derived therefrom under pressure greater than atmospheric during some stage of conversion upto the time that the molded composition is flnishedand ready'to be tabletted and/or molded under pressure. In the present invention I seek to advance the reaction and impregnation ofv cellulose further during the processing,'involving'the use of pressures usually less than ordinary molding pressures but, nevertheless, suflicient to improve impregnation of the cellulose with the urea resinand to react it further to such extent as desired, probably with the occurrence of more or less combination of the resin with the-cellulose toform a cellulosate. I

As noted above, translucency is a highly important property and the operation of treating under an intermediate pressure or prepressure prior to molding tends to improve the translucency of the molded article.

Stated in its simplest terms, the preferred em bodiment of the present invention involves a process for treating cellulose compositions withurea resin bodies under' superatmospheric pressure prior to molding or tabletting (preforming) and molding; in other words, prior to the final stages of shaping to tablet and molded forms.

The following examples are given to illustrate the invention as set forth above, it being understood that they are not to be considered as limiting. Parts are by weight.

Emmple 1.-363 parts of 37% aqueous formaldehyde and.315 parts of alpha cellulose in flock iqrm were mixed in a machine of the doughmixing type for 15 minutes at roonr temperature. 180 parts of urea were added and the'wholemixed for 1 hour further. The mix was then passed six times through milling rolls at C. After this treatment it was in the form of thin whitish-gray flakes. The material wasdried', ground to a powder, and incorporated with 1 cc. of glycerol di-..

chlorohydrin and 0.5 g. of zinc stearate per 100 g. of powder by grinding further in a ball mill."

The resulting composition, which had a density of 0.77 g. per cc., was molded at 140 C. at a pressure of 3000 pounds per square. inch for 2 minutes, a light-colored, highly glazed, mechanically strong 'molding in the form of a cup being obtained. I

Example Z.243 parts of 37% aqueous formaldehyde'and 180 parts of alpha flock were churned in a mixer for minutes. 90 parts of urea and 1.8 parts (0.5%) of zinc'stearate were added and the. whole mixed further for 1 hour. The mix was then hot-rolled four times, replaced in the mixing machine with 3.6parts of glycerol dichlorohydrin and mixed for 2 hours further. It was hot-rolled again eight times and the flakes which were formed were air-dried and ground in a ball mill.

The resulting powder was molded at 140 C.,

3000 pounds per square inch, for 1% minutes. A light colored cup was produced which possessed a highly glazed surface. Emmple 3.--180 parts oi alpha flock (equivalent to 50% illler based on the resin) and 243 parts of 37% formaldehyde were mixed in a dough mixer for minutes. 90 parts of urea and 1.8 parts of zinc stearate (0.5%) were added and the' mass mixed for 2 hours, when 3.6 parts of dichlorohydrin were added and the whole mixed for 2 hours more. The batch was denslfled between rollers at 95 C. by rolling ten times. The flakes thus obtained were dried at 35 C. for 2 hours.

The composition was-molded at 142 0., using a,

pressure oi 3000 pounds persquare inch for 1% minutes. A homogeneous, lightcoloned, highly glazed molding was obtained. The molding (which was a cup-shaped article) possessed considerable flexibility and springiness when ejected from the mold.

Example 4.-160 parts of alpha flock which had a pH of 5.5 and 241 parts of 37% formaldehyde (containing 0.06% acid calculated as formic) were churned together in a mixer for 10 minutes. The pH oi'.the mix was 5.0. The wet mass was stored in an air-tight container for 48 hours when the pH was found to be 6.0. It was then mixed for 15 minutes with 120 parts of urea, and stored for 24 hours further in an air-tight container. The pH oi the composition at this point was 6.7. 3.3 parts of dichlorohydrin and 2 parts of zinc stearate were mixed in for minutes, the pH being 6.2. The whole was hot-rolled nine times, dried aisae'n" was 6.7. The temperature throughout the above operations was 15C. 2 parts or zinc stearate and 3.3 parts ofglycerol dichlorohydrin were added and the whole was passed through heated rolls flve times. The composition was dried at room temperature overnight and the pH was found to be 6.5.

The product was molded at 125 0., 3000 pounds per'square inch, for 3 minutes, and again at 118 C. for 5 minutes. The moldings were light colored, had a moderately glazed surface, and were homogeneous. They had no tendency to stick to the mold. The composition had a medium flow.

Example 6.1B8 parts of alpha flock (pH=6.5) and 241 parts of 37% formaldehyde (pH less than 2) were mixed for 10 minutes in a mixing machine. After mixing the pH was 5.0. 120 parts of urea were added and mixed in for 15 minutes (pH=6 after mixing). 2 parts of zinc stearate and 3.3 glycerol dichlorohydrin were incorporated and the whole hot-rolled flve times.

After drying a composition having a pH of 6.7 was obtained. This was molded at 125 C., 3000 pounds per square inch, for 3 minutes. Lightcolored, highly glazed, mechanically strong moldings were obtained.

Example 7.-280 parts of 37% aqueous formaldehyde were adjusted to a pH oi 7.0 with sodium hydroxide and boiled under reflux with 138 parts of urea for 35 minutes, more caustic being added to keep the pH at 7.0 after the boiling started.

160 parts of alpha flock were placed in an autoclave, warmed to 70 C., and a vacuum of 22 inches of mercury was gradually applied and held .i'or 5 minutes. The vacuum was released and the resin syrup prepared as described in the preceding paragraph was run in, the temperature being 82 C. A 20-inch vacuum was again applied with stirring of the flock and resin mixture. Air at 50 pounds per square inch gage pressure was then allowed to enter the autoclave to create a good impregnation pressure, this pressure being subsequently released, the mix removed, and dried for 16 hours at 50 C. The composition was ball milled for 1 hour, screened, and reground with 1 cc. of glycerol dichlorohydrin and 0.35 g. of zinc stearate per 100 g. of composition.

When molded at 140 C., 3000 pounds per square inch, for 5 minutes, a white, translucent article was produced. The flow of the material was very good.

Example 8.-Example 7 was repeated, except that the 50 pounds of air pressure was not applied, but instead the autoclave was simply opened to create atmospheric pressure, the mix removed and dried; the further treatment being as in Example 7.

The composition was molded at 140 C., 3000 pounds per square inch, for 5 minutes. A lightcolored, homogeneous, moderately translucent cup was obtained. The translucency was not as perfeet as that of a molding obtained under Example 7. The flow of the composition, however, was excellent. 1

Example 9.--The procedure of Example 7 was repeated, except that neither vacuum nor pressure was applied, the syrup merely being mixed with the filler at atmospheric pressure.

Upon molding this composition at 140 C., 3000 pounds per square inch, for 5 minutes, a light blue-gray, homogeneous article was obtained, showing goodflow. The translucency, while fair, appeared to be less than that of articles obtained by both Examples 7 and 8.

Example 10.160 parts of alpha flock, 280 parts 01' 37% commercial aqueous formaldehyde, and 0.3 part oi magnesium carbonate were thoroughly mixed together for minutes. A mix which had a pH of 5.5 was obtained, and to this was added 138 parts of urea, 2 parts of zinc stearate, and 4 parts of glycerol dichlorohydrin. The whole was then subjected to rolling attrition by passing ten times through rolls at a temperature of 0., dried at room temperature overnight and i'urther at 45 C. in a current of air for 2 hours. q

The composition was molded at C., 3000 pounds per square inch, for 5 minutes and also for 7 minutes. Strong, light-colored, well-formed cups were obtained which were unaffected when boiled in water for 10 minutes.

Ezcample 11.280 parts of 37% formaldehyde (pH 7.0) and 138 parts urea were heated under a reflux condenser and started to boil after 12 minutes. After boiling for a period of 30 minutes the pH was 6.0. 2.2 parts glycerol dich-Iorohydrin were then added and the syrup was then poured over parts of alpha flock (pH 6.5) forming a mass having a pH of 6.5. This was air-dried at room temperature for 24 hours and further dried Light-colored, uniform, glazed, well-formed moldings were obtained.

What I claim is:

1. In the art 01 making cellulose and urea aldehyde resin molding compositions, the steps which comprise efiecting impregnation oi the cellulose with an aqueous urea-aldehyde resin initial condensate and subsequently subjecting the impregnated material to the action of rolling attrition pressure at a temperature precluding precuring oi the resin prior to shaping to approximately final form for molding.

2. In the art of making cellulose and ureaformaldehyde resin molding compositions, the steps which comprise effecting impregnation of the cellulose with an aqueous urea-formaldehyde resin initial condensate. subsequently subjecting the impregnated material to the action of rolling attrition pressure at a "temperature precluding precuring of the resin prior to molding and pulverizing the pressure-treated material.

CARLETON mus. 

